1. Field of the Invention
The present invention relates to techniques to excite a circularly polarized antenna and, more particularly, to a circularly polarized antenna having a QUAD-EMC unit structure.
2. Description of Related Art
In the application field of mobile communication (such as the communication between mobile phone and base station), the mobile communication end point (e.g. mobile phone) in any state (for example, mobile phone is held horizontally or vertically by the user) must completely receive the signal coming from the fixed part (e.g. the base station) so it usually makes use of a circular polarized (CP) signal.
The circularly polarized antenna nowadays has structure of a single polarized antenna element, as shown in FIG. 1A. The polarized antenna element 11 electrically connects to the conducting bar 111 with a function of distributing signals, and the conducting bar 111 electrically connects to a signal distributor, which is not shown in the figure. Besides, the two diagonal corners of the polarized antenna element 11 are chamfered to transmit and receive the circular polarized signal, which is the so-called “chamfered-corner treatment”.
However, the CP antenna of this structure is used in conjunction with a narrow bandwidth, which can not be adjusted according to the need in reality. Besides, the gain of this kind of CP antenna is restricted, so it is unable to fit in with the strict requirement of a mobile communication module (e.g. the antenna module of a mobile phone).
Moreover, compared with the above mentioned circularly polarized antenna having the single polarized antenna element, the circularly polarized antenna with a QUAD-EMC unit structure has the following advantages: (1) the gain is better still; (2) adjusting the relative position among every composed polarized antenna can improve the directivity of the transmitted polarized signal and modify the distributing situation of bandwidth.
FIG. 1B is a schematic drawing of a prior art polarized antenna having the QUAD-EMC unit structure. The polarized antenna comprises a grounding substrate 15 and four polarized antenna elements 121, 122, 123, and 124 on its surface. These polarized antenna elements electrically couple with a square conducting plate 13, which has a function of distributing signals, under the bottom surface of substrate 15, and the conducting plate 13 electrically connects to a signal distributor (not shown in the figure) through the conducting bar 14. When the polarized antenna is in a transmitting state, an electrical signal from the signal distributor is sent to the conducting bar 14, where it passes through the square conducting plate 13, and finally is sent to the polarized antenna elements 121, 122, 123, and 124. Then, the polarized antenna elements 121, 122, 123, and 124 transform the electrical signal into a wireless linear polarized (LP) signal and transmit to the environment. When the polarized antenna is in a receiving state, the polarized antenna elements 121, 122, 123, 124 receive the wireless linear polarized (LP) signal from the environment and transform it into an electrical signal. Then the electrical signal is sent to the square conducting plate 13, where it passes through the conducting bar 14, and finally is sent to the signal distributor.
Although the polarized antenna with the QUAD-EMC unit has such advantages, it can transmit and receive only the linear polarized signal, not the circular polarized signal. Hence, this polarized antenna with the QUAD-EMC unit cannot be applied in a mobile phone or any antenna module of mobile communication apparatus.
Therefore, it is desirable for the industries to provide a circular polarized antenna, which not only can transmit and receive the circular polarized signal, but also has a structure of the QUAD-EMC unit, to improve the performance of the mobile phone or any antenna module of mobile communication apparatus.